I think the idea of 'breaking the law of Iraq' is born from the natural law concept that a government must at the very least treat it's people as more than base animals, and not purposefully invade and attack their basic human rights. This includes the right to life.

So in a natural law sense, he broke one of the basic tenets of governance. The people of Iraq have now formed a government that they feel has the power and right to enforce at least those basic natural laws against violations even in times before the actual new government existed.

Further, while the concept of ex post facto laws being disallowed is a basic tenet of our legal system, that does not mean that it necessarily is a basic tenet of their new legal system.

Finally, others have already commented on the difference between guilt and proof of guilt. To those that have an issue with the statement made by the HRW, note that they are not saying he isn't guilty, nor is anyone in this thread. They're not even saying that there isn't ample evidence available to prove that he is guilty of the crimes charged. They're saying that the facts have not been presented to the court in an adequate manner so that the defense can at least make their statement. The trial has not been run in a manner that would equate to a fair system. At the very least, the judge should officially state that he is taking judicial notice of the evidence that exists outside the courtroom. Then the defense could make their statement, Saddam can be fairly judged guilty, and then hung like he should be.

It's just a matter of going through the motions, sure, but this is setting an example for the Iraq judiciary and government, as well as being a focus for the rebuilding of a nation. They could at least start by demanding a proper process before evoking retribution. Popular retribution for unexamined and untried crimes seems to be something that area already has too much of.